In the prior art, various metallurgical processes and apparatus have been proposed for extrusion of metals such as aluminum or aluminum alloys. In addition, apparatus have been proposed to clad or bond metal to the surface of an extruded product. By cladding a metal onto an extruded product, a combination of desired properties can be achieved. The base metal can be selected for cost or structural properties with the cladding metal added for other properties such as surface protection, electrical conductivity or to facilitate bonding in joining processes such as welding or brazing.
U.S. Pat. Nos. 3,095,973 and 3,137,389 to Buigne disclose extrusion cladding apparatus. Each of these patents provides a billet of material which is extruded onto the surface of a tube or core. The cladding metal may be aluminum and may range from 0.01 inches to 0.02 inches or more in thickness.
U.S. Pat. No. 4,715,207 to Rudolph discloses another extrusion device for extruding a cladding onto a core. The core may be any suitable elongated metallic article with the sheath extruded onto the outer surface of the core being aluminum or an aluminum alloy.
Other alternative methods proposed for coating or cladding extruded products include flame spraying methods. In these processes, a metal powder is passed through a high temperature flame to splatter molten droplets of the metal o the surface of the extruded product.
Disadvantages associated with prior art devices designed for extrusion cladding of extruded products include non-continuous process operation. In the apparatus of Buigne, the process has to be stopped to replace the butt of the cladding billet with a new billet. Moreover, the cladding thickness range is limited as a result of performing the cladding using an extrusion process.
Cladding of extruded products using flame spraying techniques are disadvantageous in that the flame spraying operation is performed downstream of the extruding press. As a result, the surface of the extruded product is exposed to the atmosphere prior to the flame spraying operation, such exposure contributing to oxidation of the surface which effects the quality of the adhesion between the extruded product and cladding material. In addition, the flame spraying processes produce a rough or textured surface on the extruded products.
In response to the deficiencies in prior art apparatus and methods for cladding of extruded product, a need has developed to provide an improved apparatus and method for cladding extruded forms.
In response to this need, the present invention provides an improved method and apparatus for continuous molten metal cladding. The present invention provides improved adhesion between cladding metal and an extrusion by reducing or eliminating oxidation of the surface of the extruded product between the extrusion step and the molten metal cladding step. In addition, by using a molten metal cladding source, continuous smooth surface cladding may be achieved with a uniform cladding thickness. None of the prior art discussed above teaches or fairly suggest all of the aspects of the inventive method of and apparatus for a continuous molten metal cladding of elongated members such as extrusion products.